Generator of a mechanical foam for fire extinguishing purpose



1964 LYDlE ROTVAND 3,117,629

BORN ZELENSKY GENERATOR OF A MECHANICAL FOAM FOR FIRE EXTINGUISHING PURPOSE Filed March 7. 1961 tot United States Patent Ofiice 3,ll7,fi2 Patented Jan. 14, 1964 3,117,629 GENERATOR OF A MECHANICAL FOAM FOR FIRE EXTINGUISHING PURPOSE Lydia Rotvand, born Zelensky, 4 Rue Octave Feuillet, Paris, France Filed Mar. 7, 1961, Ser. No. 94,028 Claims priority, application France Apr. 7, 1960 4 Claims. (Cl. 169-15) The present invention relates to a generator for the production of mechanical foam, that is to say a foam obtained by incorporating air in water with an emulsifier: these generators include essentially a mixing tube to one end of which the water mixed with an emulsifier is added under pressure, this liquid jet sucking the air through side ports provided in the tube near the injector.

The invention aims at obtaining a jet concentrated and having a long range of a fine and homogeneous foam by increasing the hydrodynamic and aerodynamic efficiency of the apparatus.

One knows that the formation of a foam having a fine and homogeneous contexture is improved by the turbulence of the fiow of the mixture of air and water in the tube and, to increase this turbulence many means have been proposed, particularly anti-splash devices disposed at the outlet of the injector, scattering helices, meshes or grids, multiple injectors to produce several intersecting jets running against the wall of the mixing tube, directing blades to impart to the jet a rotary mo tion round its axis, or Wrinkles on the Wall of the tube. These means, which often are used in various combinations, supply effectively a foam having the required quality but they have the drawback of absorbing, by friction and losses of head, an appreciable fraction of the energy of the jet, the range of which is thereby strongly reduced.

In another connection, it has already been proposed to produce a turbulent flow for the formation of the foam Without using mechanical means which give rise to important losses of energy. One can show easily that, when the foam fills up entirely the cross section of the mixing tube, the flow becomes necessarily turbulent, allowance being made for the speed of the flow and for the viscosity of the mixture, as a laminar or streamlined flow can only arise at much smaller flow speeds.

Based upon this notion, it has been proposed to give to the mixing tube a sufficient length for its cross section, which is entirely filled up with the primary emulsion, that is to say a coarse foam consisting of large bubbles, so that, during the passing through the tube, the foam becomes sufiiciently fine and homogeneous under action of the fairly natural turbulence of the flow. Nevertheless, a satisfactory result requires the tube to have a length at least equal to fifty or sixty times its diameter and this, for tubes having a large cross section, would lead to prohibitive lengths. To meet this drawback, it has already been proposed to increase, on a given length, the cross section of the tube, thereby creating a back-pressure which causes the cross-section of the tube entirely filled by the foam to be shifted back towards the inlet thereof, thus making it possible to reduce accordingly the length of the tube, a subsequent narrowing of the tube making it possible to obtain a sufficient discharge speed for the jet.

The present invention makes it possible, by the working of the principle of natural turbulence above described, to obtain the same satisfactory result but with much shorter mixing tubes and even more simple means.

According to the invention, the delivery tube is characterized by the fact that it includes, to increase the toric turbulence of the flow, a small, slightly converging pipe which is mounted inside the tube and is coaxially supported by radial blades or by any other means and is intended to increase the speed of the central part of the jet and reduce the speed of its peripheral part, this pipe being disposed in a zone of the tube where its cross section is entirely filled up with the foam.

One understands that, under action of the converging axial pipe, the speed of the central part of the jet is increased while the speed of its annular peripheral part is slowed: a speed difference, generating a toric turbulence, is produced between the two central and annular jets. In practice, this does not result in any loss of energy as this modification imparted to the flow only transforms a potential energy into kinetic energy and conversely, the energy remaining always available and this transformation being reversible in case of need.

The existence of the turbulence thus created can be observed at the output end of the tube where it produces a whirling jet which tends to break up laterally. When the generator is intended to feed a rather long piping at the end of which is a Water hose nozzle, this defeet is of little importance because, during the flowing of the foam through the piping, the speeds in the different parts of the section tend to become even. On the contrary, if the generator is intended to act at the same time as a hose-nozzle to force out the foam, as a free jet at a long range, the mixing tube, according to the invention, includes, near its outlet end, a second slightly diverging pipe intended to make uniform the speed of the fiow in all the cross section of the tube and to suppress the turbulence in the foam jet discharged by the apparatus.

By way of example, a generator provided with a hose nozzle according to the invention is described hereafter and illustrated in the annexed drawing.

FIGURE 1 is an axial section.

FIGURE 2 is a cross section along I I-II of FIG- URE 1.

FIGURE 3 is another cross section along III-III of FIGURE 1.

The apparatus illustrated in the drawing is constituted by a tube 1 having along its entire length a constant useful section. At the rear, the apparatus includes an admission pipe 2 for the water under pressure ending in a cylindrical or very slightly diverging injection nozzle 3 in which enters a converging nozzle 4 forming the end of a tube 5 axially disposed in the pipe 2 and used for the suction of the emulsifying agent.

Suction ports for the air, 6, 6', 6" (four, for instance), are provided in the tube 1 immediately downstream of the injection nozzle 3.

At a rather small distance from the injection nozzle 3, but sufficient for the corresponding cross section of the tube 1 to be already entirely filled up by the formation of primary foam, and in which consequently the stream is turbulent, pipe 9 having the shape of the frustum of a cone converging in the direction of the flow of the foam; the said pipe 9 is held in position (FIGS. 1 and 2) by radial blades 10, 10, 10", 10" and cre eates a central narrowing passage 11 an an annular peripheral expanding passage 11', thus allowing the speed in the central part of the liquid stream to increase and serving to slow down the speed of the peripheral part of the liquid stream, consequently increasing the turbulence. Preferably, the frusto-conical pipe 9 converges slightly in the direction of the flow of the emulsified stream of water. For instance, the slope of the walls of this frusto-conical pipe ranges between 3 and 5 and the diameter of the small base of the frusto-conical pipe 9 is, for example, equal to half the diameter of the tube 1, while the length of the frusto-conical pipe 3 9, is for instance, equal to the diameter of the tube 1. To keep unchanging the passage section of the team, the diameter of the length 1' or the tube 1 in which is mounted the cone 9 is slightly increased to compensate for the section decrease resulting from the thickness of the wall of the cone and of the tln'ckness of the blades.

Near the outlet end or" the tube 1, in a length 1" having an increased diameter for the reasons above mentioned, is mounted a second pipe 12, on blades 13, 13', this pipe 12 is divergent and intended to restore in the two, central and peripheral, parts of the foam stream, similar speeds before the projection of the stream through the projecting pipe 14. Thanks to this divergent cone, the peripheral annular stream, previously slowed down by the cone 9, passes through a restricted passage 15 whereas the central stream, accelerated by the cone 9, passes through an expanded passage 15. The pipe 12 diverges in the direction of the flow of the foam and it has the form of the frustum of a cone having a slope of about 3. The diameter of the small base of this frustoaconical pipe 12 is equal to the small base of the frusto-conical pipe 9, and thereby to half the diameter of the tube 1, while the length of the frusto-conical pipe 12 is equal to two or three times the diameter of the tube 1.

To obtain a foam having the same specifications and the same quality, the application of the characteristics which are the object of the above described invention makes it possible to shorten in a ratio of about 2.5 the length of an even tube which would be necessary for the formation of the foam by means of a natural toric turbulence.

What I claim is:

l. A generator for the production of a mechanical foam comprising a mixing tube having a substantially constant cross section, a single central injector disposed at one end of the tube and adapted to inject therein water under pressure admixed with an emulsifying agent in the form of a divergent stream filling the said tube at a transverse plane located at some distance from said injector, a single set of apertures provided in the wall of the tube and located between said injector and the said transverse plane for inducing air in said tube and a small conical pipe slightly converging in the direction of the flow of the emulsified stream of water filling up said tube and mounted therein, the said pipe having an inlet passage which is smaller than the transverse section of the tube to define therewith for the said stream a central passage of decreasing cross sections in the direction of the how and a peripheral passage of increasing cross-sections, whereby the central part of the stream is accelerated while the peripheral part is slowed down and the toric turbulence of the flow is increased,

2. A generator for the production of a mechanical foam comprising a mixing tube having a substantially cross section over its length, a single central injector disposed at one end of the tube and adapted to inject therein water under pressure admixed with an emulsifying agent in the form of a divergent stream filling the said tube at a transverse plane located at some distance from said injector, a single set of apertures provided in the wall of the tube and located between said injector and the said transverse plane for inducing air in said tube, a first small conical pipe slightly converging in the direction of the flow of the emulsified stream of water filling up said tube and mounted therein, the said first pipe having an inlet passage which is'smaller than the transverse section of the tube to define therewith for the said stream a central passage of decreasing crosssections in the di rection of the flow and a peripheral passage of increasing cross-sections, whereby the central part of the stream which passes through said first pipe is accelerated while the peripheral part is slowed down and its toric turbulence is increased, and a second small conical pipe diverging in the direction of the flow and disposed in the said tube in the vicinity of its outlet end, the said second pipe having an outlet passage which is smaller than the cross-section of the tube whereby a peripheral passage around said second pipe is forrned having crosssections decreasing in the direction of the flow of the stream of emulsified water whereby the said turbulence is suppressed before the foam is discharged from the tube.

3. A generator for the production of a mechanical foam according to claim 2, in which the said first conical pipe has an apex angle ranging about 3 to 5, an outlet diameter equal to half the diameter of the tube and a length equal to said diameter of the tube.

4. A generator for the production of a mechanical foam according to claim 2., in which the said second conical pipe has an apex angle of about 3, an inlet diameter equal to half the diameter of the tube and a length comprised between twice and three times said diameter or the tube.

References {Iited in the file of this patent UNITED STATES PATENTS 1,108,247 Schenck Aug. 25, 1914 2,577,451 Clemens et al. Dec. 4, 1951 2,630,183 Foutz Mar. 3, 1953 2,704,089 Woodworth Mar. 13, 1955 2,761,516 Vassilkovsky Sept. 4, 1956 FOREIGN PATENTS 969,293 France May 17, 1950 

1. A GENERATOR FOR THE PRODUCTION OF A MECHANICAL FOAM COMPRISING A MIXING TUBE HAVING A SUBSTANTIALLY CONSTANT CROSS SECTION, A SINGLE CENTRAL INJECTOR DISPOSED AT ONE END OF THE TUBE AND ADAPTED TO INJECT THEREIN WATER UNDER PRESSURE ADMIXED WITH AN EMULSIFYING AGENT IN THE FORM OF A DIVERGENT STREAM FILLING THE SAID TUBE AT A TRANSVERSE PLANE LOCATED AT SOME DISTANCE FROM SAID INJECTOR, A SINGLE SET OF APERTURES PROVIDED IN THE WALL OF THE TUBE AND LOCATED BETWEEN SAID INJECTOR AND THE SAID TRANSVERSE PLANE FOR INDUCING AIR IN SAID TUBE AND A SMALL CONICAL PIPE SLIGHTLY CONVERGING IN THE DIRECTION OF THE FLOW OF THE EMULSIFIED STREAM OF WATER FILLING UP SAID TUBE AND MOUNTED THEREIN, THE SAID PIPE HAVING AN INLET PASSAGE WHICH IS SMALLER THAN THE TRANSVERSE SECTION OF THE TUBE TO DEFINE THEREWITH FOR THE SAID STREAM A CENTRAL PASSAGE OF DECREASING CROSS SECTIONS IN THE DIRECTION OF THE FLOW AND A PERIPHERAL PASSAGE OF INCREASING CROSS-SECTIONS, WHEREBY THE CENTRAL PART OF THE STREAM IS ACCELERATED WHILE THE PERIPHERAL PART IS SLOWED DOWN AND THE TORIC TURBULENCE OF THE FLOW IS INCREASED. 